This invention relates to fertilizer products and more particularly to a method of making a commercial fertilizer product which utilizes the dross waste product of scrap aluminum resmelting and purification operations.
In the various non-ferrous smelting operations, it is conventional to use a fluxing material not only to facilitate the fusion of the metal but to react with and remove many of the contaminating metallic impurities normally present in scrap aluminum. Among these impurities are traces of organic matter present as residues of plastics, fabrics of labels if the scrap metal is from old lawn furniture. Other impurities would be the labels printed directly upon aluminum containers such as beer cans. Scrap aluminum from automobile scrap metal is frequently contaminated with various lubricants or other organic accumulations. Scrap aluminum metal also includes metallic impurities that are preferably removed from the aluminum metal in the fluxing process. The metallic impurities, normally removed in this purification process, include a great many varieties of the so-called trace metals. Among these are the more common zinc, copper, iron, calcium, lead, and magnesium, and less common manganese, molybdenum, boron, sulfur, selenium, and the much more rare impurities including chromium, arsenic, silver, cadmium, and mercury. Even traces of platinum are not uncommon.
Whereas organic contaminant are usually eliminated by the combustion temperatures employed, the trace metal contaminates are trapped by the flux and eventually removed by skimming off the dross so produced. The fluxing material is usually a blend of sodium and potassium chlorides to which approximately five percent of cryolite (sodium aluminum fluoride) is added to promote melting of the scrap aluminum charged to the furnace for smelting. The ratio of potassium chloride to sodium chloride may also vary as required. Conventionally the amount of fluxing material used can vary widely depending upon the composition of the scrap aluminum to be processed. Typically, the flux amounts to about ten percent of the metal scrap charged to the furnace or metal bath. The fluxing material can be added to the molten metal immediately before, during, or immediately after the charging of the metal scrap. It is conventional to use a compressed air "lance" to thoroughly agitate the flux with the molten metal until the reaction is complete. At that point the flux containing the trapped metal impurities remains in a semifluid condition and floats on the surface of the molten aluminum metal. This dross can then be removed by skimming.
It is desirable to remove as much as possible of the magnesium which is usually present in amounts of less than one percent. This is done by gassing the molten metal with a chlorine "lance" to convert the magnesium into its chloride which is volatilized at furnace temperatures of 1500.degree.-1600.degree. F. Some aluminum chloride is formed and volatilized as well.
One experienced in the art of resmelting scrap metal is familiar with numerous other modifications that may be employed including the addition of small amounts of caustic soda, alkali silicates and other additives to improve subsequent handling of the skimmed dross or improve the purification process being effected by the fluxing operation.
In any case, the dross is removed by skimming and allowed to solidify in large chunks, usually in iron or steel containers, for subsequent processing. The subsequent processing comprises the separation of recoverable aluminum for resmelting, and disposal of the waste dross product. This processing includes grinding the solid waste dross into a powder form, from which aluminum flakes are separated by a screening operation.
Disposition of the powdered waste dross remaining after the screening operation presents several problems. The volume of such dross can amount to hundreds of tons per day, and is therefore a disposal problem of some magnitude. Further, the powdered waste dross is extremely dusty. The actual cost of disposal for such large tonnages of waste material is a major expense item and has been so for many years.
Accordingly, it is a general object of the present invention to provide a new method of disposing of waste dross that avoids the problems associated with conventional disposal methods.
A further object is to provide a process for converting the dross from a disposable waste product into a salable commodity having a value on its own.
A more particular object is to provide an economical process for converting waste dross into chemical fertilizer of commerical value.
Other objects and advantages of the present invention will become apparent to those skilled in the art upon reading the following detailed description. Although specific procedures are used to describe the preferred embodiment of my invention, I do not wish to be limited thereby. On the contrary, I wish to cover the various obvious alternatives and equivalents which may be included within the spirit and scope of the appended claims.